Three-component aluminum-titanium tetrahalide catalysts for olefin polymerization



United States Patent 3,026,309 THREE-COMPONENT ALUMINUM-TITANIUM TETRAHALIDE CATALYSTS FGR OLEFIN POLYMERIZATION Harry W. Coover, 51:, Kingsport, Tenn., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Mar. 31, 1958, Ser. No. 724,899 12 Claims. (Cl. 260-937) This invention relates to a new and improved polymerization process and is particularly concerned with the use of a novel catalyst combination for preparing high molecular weight solid polyolefins, such as polypropylene, of high density and crystallinity. In a particular aspect the invention is concerned with the preparation of polypropylene and higher polyolefins having a high crystallinity and a high density using a particular catalyst combination which has unexpected catalytic activity.

Polyethylene has heretofore been prepared by high pressure processes to give relatively flexible polymers having a rather high degree of chain branching and a density considerably lower than the theoretical density. Thus, pressures of the order of 500 atmospheres or more and usually of the order of 1000-1500 atmospheres are commonly employed. It has been found that more dense polyethylenes can be produced by certain catalyst com binations to give polymers which have very little chain branching and a high degree of crystallinity. The exact reason why certain catalyst combinations give these highly dense and highly crystalline polymers is not readily understood. Furthermore, the activity of the catalysts ordinarily depends upon certain specific catalyst combinations, and the results are ordinarily highly unpredictable, since relatively minor changes in the catalyst combination often lead to liquid polymers rather than the desired solid polymers.

In my copending application Serial No. 559,536, filed January 17, 1956, now abandoned, of which this application is a continuation-in-part, there is described the polymerization of :z-monoolefins to produce dense, highly crystalline polymers by heating said monoolefins in the presence of a mixture of aluminum and a titanium tetrahalide. Also in my copending application Serial No. 711,139, filed January 27, 1958, which is also a continuation-in-part of application Serial No. 559,536, there is described the polymerization of a a-monoolefins to form dense crystalline polymers by polymerizing said monoolefins in the presence of a catalyst formed by heating a mixture of aluminum and a titanium tetrahalide in the absence of a polymerizable hydrocarbon. This latter catalyst can be termed a preactivated catalyst and the former catalyst can be termed an unactivated catalyst. The preactivated catalyst has been found to produce un expectedly superior results when compared with the unactivated catalyst. Both the unactivated and the preactivated catalysts are particularly useful for polymerizing ethylene to form dense crystalline polymers, but these catalysts can also be used for polymerizing propylene and higher m-monooleiins to form dense crystalline polymers. However, when the unactivated and preactivated catalysts are used to polymerize propylene and higher a-monoolefins it has been found that the polymeric product contains substantial amounts of relatively low molecular weight polymers which are either greases, oils or rubbery products. Gbviously, when a high molecular weight, dense crystalline product is desired, these relatively low molecular Weight polymers are undesirable, and it is one of the purposes of this invention to polymerize propylene and higher a-monoolefins in the presence of an improved catalytic mixture wherein the formation of relatively low molecular Weight polymers is substantially and unexpectedly reduced.

It is an object of this invention to provide a novel and improved process for polymerizing propylene and higher a-monooleiins and in doing so to overcome disadvantages of earlier procedures. it is a particular object of this in vention to provide a novel and improved process for polymerizing propylene in the presence of an improved catalyst composition containing aluminum and a titanium tetrahalide. As a result of the use of this improved catalyst composition unexpectedly improved yields of solid, dense, crystalline polymer are obtained without the cencomitant formation of substantial amounts of lower molecular weight polymer. Other objects of this invention will be apparent from the description and claims which follow.

The above and other objects are attained by means of this invention, wherein a-monoolefins, either singly or in admixture, are readily polymerized to high molecular weight solid polymers by effecting the polymerization in the presence of an unactivated or a preactivated aluminum-titanium tetrahalide catalyst composition containing a compound of a group VA element having the formula R Z wherein Z is a group VA element selected from the group consisting of nitrogen, phosphorus, arsenic and antimony and each R is a radical selected from the group consisting of hydrogen and hydrocarbon radicals containing 1-12 carbon atoms and selected from the group consisting of alkyl, aryl and aralkyl. Among these hydrocarbon radicals are methyl, ethyl, propyl, 'butyl, octyl, dodecyl, phenyl, phenylethyl and naphthyl. In the group VA compound the three radicals represented by R can be the same or different. The significantly improved yields of the crystalline polymers produced with the above catalyst were completely unexpected. The inventive process can be cmied out in liquid phase in an inert organic liquid and preferably an inert liquid hydrocarbon vehicle, but in some instances the process is operated without a solvent. The process proceeds with excellent results over a temperature range of from- 0 C. to 250 C. although it is preferred to operate within the range of from about 50 C. to about C. Likewise, the reaction pressures may be varied widely from about atmospheric pressure to very high pressures of the order of 20,000 p.s.i. or higher. A particular advantage of the invention is that pressures of the order of 30-1000 p.s.i. give excellent results, and it is not necessary to employ the extremely high pressures which were necessary heretofore. The liquid vehicle employed is desirably one which serves as an inert liquid reaction medium.

The invention is of particular importance in the preparation of highly crystalline polypropylene although it can be used for polymerizing mixtures of ethylene and propylene as well as other a-monoolefins containing up to 10 carbon atoms. The results obtained by polymerizing the various olefins are quite unexpected. The crystallinity of the polymer as well as the average molecular Weight of the product are substantially and unexpectedly improved. The high molecular weight, high density polymers of this invention are insoluble in solvents at ordinary temperatures but they are soluble in such solvents as xylene, toluene or tetralin at elevated temperatures. These solubility characteristics make it possible to carry out the polymerization process under conditions wherein the polymer formed is soluble in the reaction medium during the polymerization and can be precipitated therefrom by lowering the temperature of the resulting mixture. The polypropylene produced by practicing this inven tion has a softening point above C. and a density of 0.91 and higher. Usually the density of the polypropylene is of the order of 0.91 to 0.92.

The polypropylene and other polyolefins prepared in U accordance with the invention can be molded or extruded and can be used to form plates, sheets, films, or a variety of molded objects which exhibit a higher degree of stiffness than do the corresponding high pressure polyolefins. The products can be extruded in the form of pipe or tubing of excellent rigidity and can be injection molded into a great variety of articles. The polymers can also be cold drawn into ribbons, bands, fibers or filaments of high elasticity and rigidity. Fibers of high strength can be spun from the molten polypropylene obtained according to this process. Other poly-wolefins as well as copolymers of ethylene and propylene can also be prepared in accordance with this invention.

As has been indicated above the improved results obtained in accordance with this invention depend upon the particular catalyst combination. Thus, one of the components of the catalyst is aluminum and another component is a titanium tetrahalide wherein the halogen is selected from the group consisting of chlorine, bromine and iodine. The third component of the catalyst composition is a compound of a group VA element having the structural formula R 2 wherein Z is a group VA element selected from the group consisting of nitrogen, phosphorus, arsenic and antimony. Each R is a radical selected from the group consisting of hydrogen and hydrocarbon radicals as defined hereinabove. In this third component the R radicals can be the same but in some instances dififerent radicals are used. Among the specific compounds that can be used are tributylamine, diethylaniline, tributyl phosphine, triphenylphosphine, triphenylarsine, triphenylstibine and the like.

The limiting factor in the temperature of the process appears to be the decomposition temperature of the catalyst. Ordinarily temperatures from 50 C. to 150 C. are employed, although temperatures as low as 20 C. or as high as 250 C. can be employed if desired. Usually, it is not desirable or economical to eifect the polymerization at temperatures below 20 C., and the process can be readily controlled at room temperature or higher which is an advantage from the standpoint of commercial processing. The pressure employed is usually only suiiicient to maintain the reaction mixture in liquid form during the polymerization, although higher pressures can be used if desired. The pressure is ordinarily achieved by pressuring the system with the monomer whereby additional monomer dissolves in the reaction vehicle as the polymerization progresses. The catalyst compositions of this invention, when reacted with water, do not produce hydrogen.

The polymerization embodying the invention can be carried out batchwise or in a continuous flowing stream process. The continuous processes are preferred for economic reasons, and particularly good results are obtained using continuous processes wherein a polymerization mixture of constant composition is continuously and progressively introduced into the polymerization zone and the mixture resulting from the polymerization is continuously and progressively withdrawn from the polymerization zone at an equivalent rate, whereby the relative concentration of the various components in the polyrnerization zone remains substantially unchanged during the process. This results in formation of polymer of extremely uniform molecular weight distribution over a relatively narrow range. Such uniform polymers possess distinct advantages since they do not contain any substantial amount of the low molecular weight or high molecular weight formations which are ordinarily tound in polymers prepared by batch reactions.

In the continuous flowing stream process, the temperature is desirably maintained at a substantially constant value within the preferred range in order to achieve the highest degree of uniformity. Since it is desirable to employ a solution of the monomer of relatively high concentration, the process is desirably efiected under a pressure of from to 1000 p.s.i. obtained by pressuring the system with the monomer being polymerized. The amount of vehicle employed can be varied over rather wide limits with relation to the monomer and catalyst mixture. Best results are obtained using a concentration of catalyst of from about 0.1% to about 2% by weight based on the weight of the vehicle. The concentration of the monomer in the vehicle will vary rather widely depending upon the reaction conditions and will usually range from about 2 to 50% by weight. For a solution type of process it is preferred to use a concentration from about 2 to about 10% by weight based on the weight of the vehicle, and for a slurry type of process higher concentrations, for example up to and higher are preferred. Higher concentrations of monomer ordinarily increase the rate of polymerization, but concentrations above 510% by weight in a solution process are ordinarily less desirable because the polymer dissolved in the reaction medium results in a very viscous solution.

The titanium tetrahalide in the catalyst is usually employed in an amount of from 0.1 to parts by weight per part of aluminum metal, and the molar ratio of titanium tetrahalide to the third component of the catalytic mixture can be varied within the range of 1:1 to 1:01. A particularly effective catalyst contains one mole of titanium tetrahalide and 0.25 mole of the third component per mole of aluminum. The polymerization time can be varied as desired and will usually be of the order of from 30 minutes to several hours in batch processes. Contact times of from 1 to 4 hours are commonly employed in autoclave type reactions. When a continuous process is employed, the contact time in the polymerization zone can also be regulated as desired, and in some cases it is not necessary to employ reaction or contact times much beyond one-half to one hour since a cyclic system can be employed by precipitation of the polymer and return of the vehicle and unused catalyst to the charging zone wherein the catalyst can be replenished and additional monomer introduced.

The organic vehicle employed can be an aliphatic alkane or cycloalkane such as pentane, hexane, heptane or cyclohexane, or a hydrogenated aromatic compound such as tetrahydronaphthalene or decahydronaphthalene, or a high molecular weight liquid paraflin or mixture of parafiins which are liquid at the reaction temperature, or an aromatic hydrocarbon such as benzene, toluene, xylene, or the like, or a halogenated aromatic compound such as chlorobenzene, chloronaphthalene, or orthodichlorobenzene. The nature of the vehicle is subject to considerable variation, although the vehicle employed should be liquid under the conditions of reaction and relatively inert. The hydrocarbon liquids are desirably employed. Other solvents which can be used include ethyl benzene, isopropyl benzene, ethyl toluene, n-propyl benzene, diethyl benzenes, mono and dialkyl naphthalenes, n-pentane, n-octane, isooctane,

' methyl cyclohexane, tetralin, decalin, and any of the other well-known inert liquid hydrocarbons.

The polymerization ordinarily is accomplished by merely admixing the components of the polymerization mixture which is then adjusted to the reaction temperature. The more elevated temperatures can be used to increase the solubility of polymeric product in the vehicle. When the highly uniform polymers are desired employing the continuous process wherein the relative proportions of the various components are maintained substantially constant, the temperature is desirably controlled within a relatively narrow range. This is readily accomplished since the solvent vehicle forms a high percentage of the polymerization mixture and hence can be heated or cooled to maintain the temperature as desired.

A particularly efiective catalyst for polymerizing propylene and other a-monoolefins in accordance with. this invention is a mixture of aluminum, titanium tetrachloride and tributyl phosphine. The importance of the third component of this reaction mixture is evident from the fact that the presence of the third component makes possible the production of polymers of substantially improved properties.

Tne aluminum and titanium tetrahalide that are employed in the catalytic mixture of this invention can be in either the unactivated or the preactivated form. When the unactivated form is employed the aluminum and titanium tetrahalide as well as the third component of the catalyst are added to the polymerization reaction mixture, and in most instances it is usually necessary to undergo an induction period before the monomer in the reaction mixture is actually polymerized to the desired product. Preferably the aluminum and titanium tetrahalide are employed in a preactivated form. For preactivation of the catalyst a mixture of aluminum and titanium tetrahalide is heated for varying periods of time in the absence of polymerizable monomer, such as ethylene, propylene and higher monoolefins. Temperatures of 50 C. up to about 300 C. are usually sufficient for the preactivation, and contact times varying from 5 minutes to 48 hours can be used. Suitable procedures for preparing preactivated mixtures of aluminum and titanium tetrahalide are described in my foresaid copending applications Serial No. 559,536 and Serial No. 711,189. The catalytic mixture that is formed as a result of the preactivation of aluminum and titanium tetrahalide has been found to contain aluminum trihalide and titanium trihalide in addition to aluminum and titanium tetrahalide. This mixture along with the third component of the catalyst described above is outstandingly effective for polymerizing propylene and higher monoolefins while at the same time reducing substantially the amount of low molecular weight polymers formed during the reaction. The aluminum that is employed in the catalyst mixture is preferably in flake or finely-divided form for optimum activity, rapid polymerization and high yield of polymer but actually any form of aluminum metal can be used in the process. When a granular aluminum of commerce is used it is desirable to clean the surface of the granules with an acid or acid mixtures such as a mixture of nitric and hydrofluoric acids or with a base for optimum results. However, the cleaning of the aluminum is not absolutely essential to the invention. Titanium tetrachloride is the preferred titanium tetrahalide although titanium tetrabromide as well as titanium tetraiodide can be employed in the catalytic mixture.

The invention is illustrated by the following examples or certain preferred embodiments thereof.

Example 1 In a nitrogen-filled dry box a dry 280-ml. stainless steel autoclave Was loaded with 0.75 gram of total catalyst containing a 1:1 molar ratio of activated aluminumtitanium tetrachloride and a 0.25 molar ratio of tributyl phosphine. The aluminum and titanium tetrachloride had been activated by heating the mixture in the absence of polymerizable hydrocarbon to a temperature of about 200 C. for a period of 90 minutes. The autoclave was capped, removed from the dry box and placed in a rocker. A 100-rnl. (51 grams) of propylene was added. The mixture was rocked and heated to 85 C., and maintained at that temperature for 4 hours. A 45.5-gram yield of solid polypropylene was obtained having a density of 0.913 and an inherent viscosity of 2.90. After extraction with dibutyl ether, there was left 38.7 grams of highly crystalline polypropylene having a density of 0.919 and an inherent viscosity of 3.11.

When the above run is repeated using a catalyst from which the third component has been omitted, the yield of oily polymers predominates and only about 5 grams of solid polypropylene is obtained.

Replacement of tributyl phosphine in the example with tributylarnine, diethylaniline, triphenyl phosphine, triphenylarsine and triphenyl stibine resulted in unexpected increases in the yields of crystalline polypropylene produced.

Example 2 -The process of Example l'was followed using 0.1 gram of total catalyst having a 12120.5 molar ratio of aluminum, titanium tetrachloride and tributyl phosphine at a temperature of C. 15.1 grams of solid polypropylene were produced with a density of 0.914 and an inherent viscosity of 1.95.

Example 3 The process of Example 1 was followed using 1.5 grams of catalyst having a 1:l:0.1 molar ratio of aluminum, titanium tetrachloride and triphenyl stibine at a temperature of 55 C. A 9.2-gram yield of solid polypropylene was obtained having a density of 0.914 and an inherent viscosity of 3.82.

Example 4 The process of Example 1 was employed to increase the yields of polymers formed from the following monomers: l-butene, 1-pentene, 4-methyl-l-pentene, S-methyll-butene, allyl benzene, styrene, fluorostyrene and vinyl cyclohexane.

Thus, by means of this invention polyolefins such as polypropylene are readily produced using a catalyst combination whose improved eifectiveness could not have been predicted. The polymers thus obtained can be extruded, mechanically milled, cast or molded as desired. The polymers can be used as blending agents with relatively more flexible polyhydrocarbons to give any desired combination of properties. The polymers can also be blended with antioxidants, stabilizers, plasticizers, fillers, pigments, and the like, or mixed with other polymeric materials, waxes and the like.

From the detailed disclosure of this invention it is quite apparent that in this polymerization procedure a novel catalyst, not suggested in prior art polymerization procedures, is employed. As a result of the use of this novel catalyst it is possible to produce polymeric hydrocarbons, particulaly polypropylene, having properties not heretofore obtainable. For example, polypropylene prepared in the presence of catalyst combinations within the scope of this invention is substantially free of rubbery and oily polymers and thus it is not necessary to subject such polypropylene of this invention to extraction pro cedures in order to obtain a commercial product. Also polypropylene produced in accordance with this invention possesses unexpectedly high crystallinity, and unusually high softening point and outstanding thermal stability. Such polypropylene also has a very high stiffness as a result of the unexpectedly high crystallinity. The pro erties imparted to polypropylene prepared in accordance with this invention thus characterize and distinguish this polypropylene from polymers prepared by prior art polymerization procedures.

The novel catalysts defined above can be used to produce high molecular weight crystalline polymeric hydro carbons. The molecular weight of the polymers can be varied over a wide range of introducing hydrogen to the polymerization reaction. Such hydrogen can be introduced separately or in admixture with the olefin monomer. The polymers produced in accordance with this invention can be separated from polymerization catalyst by suitable extraction procedures, for example, by washing with water or lower aliphatic alcohols such as methanol.

The catalyst compositions have been described above as being efiective primarily for the polymerization of u-monoolefins. These catalyst compositions can, however, be used for polymerizing other a-olefins, and it is not necessary to limit the process of the invention to monoolefins. Other u-olefins that can be used are butadiene, isoprene, 1,3-pentadiene and the like.

The diluents employed in practicing this invention can be advantageously purified prior to use in the polymerization reaction by contacting the diluent, for example, in a distillation procedure or otherwise, with the polymerization catalyst to remove undesirable trace impurities. Also, prior to such purification of the diluent the catalyst can be contacted advantageously with polymerizable 'tx-monoolefin.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of this invention as describer hereinabove and as defined in the appended claims.

I claim:

1. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises effecting the polymerization in liquid dispersion in an inert hydrocarbon liquid and in the presence of a catalytic mixture consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and an amine having the structural formula (R) N wherein R is a hydrocarbon radical selected from the group consisting of alkyl radicals containing 1-12 carbon atoms and phenyl, the molar ratio of titanium tetrachloride to amine being within the range of 1:1 to 1:0.1.

2. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises effecting the polymerization in liquid dispersion in an inert hydrocarbon liquid and in the presence of a catalytic mixture consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and a stibine having the structural formula (R) Sb wherein R is a hydrocarbon radical selected from the group consisting of alkyl radicals containing 1-12 carbon atoms and phenyl, the molar ratio of titanium tetrachloride to stibine being within the range of 1: 1 to 110.1.

3. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises effecting the polymerization in liquid dispersion in an inert hydrocarbon liquid and in the presence of a catalytic mixture consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and an arsine having the structural formula (R) As wherein R is a hydrocarbon radical selected from the group consisting of alkyl radicals containing 1-12 carbon atoms and phenyl, the molar ratio of titanium tetrachloride to arsine being within the range of 1:1 to 1:0.1.

4. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises efiecting the polymerization in liquid dispersion in an inert hydrocarbon liquid and in the presence of a catalytic mixture consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and triphenyl amine, the molar ratio of titanium tetrachloride and triphenyl amine being within the range of -1:1 to 110.1, the polymerization temperature being Within the range of 55-150 C. and the polymerization pressure not exceeding 1000 p.s.i.

5. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises effecting the polymerization in liquid dispersion in an inert hydrocarbon liquid and in the presence of a catalytic mixture consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and triphenyl stibine, the molar ratio of titanium tetrachloride and triphenyl stibine being within the range of 1:1 to 1:0.1, the polymerization temperature being within the range of 55150 C. and the polymerization pressure not exceeding 1000 p.s.i.

6. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises effecting the polymerization in liquid dispersion in an inert hydrocarbon liquid and in the presence of a catalytic mix-ture consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and triphenyl arsine, the molar ratio of titanium tetrachloride and triphenyl arsine being Within the range of 1:1 to 1:01, the polymerization temperature being within the range of 55-150 C. and the polymerization pressure not exceeding 1000 p.s.i.

7. As a composition of matter, a polymerization catalyst consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and an amine having the structural formula (R) N wherein R is a hydrocarbon radical selected from the group consisting of alkyl radicals containing 1-12 carbon atoms and phenyl, the molar ratio of titanium tetrachloride to amine being within the range of 1:1 to 120.1.

8. As a composition of matter, a polymerization catalyst consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and a stibine having the structural formula (R') Sb wherein R is a hydrocarbon radical selected from the group consisting of alkyl radicals containing 112 carbon atoms and phenyl, the molar ratio of titanium tetrachloride to stibine being within the range of 1 :1 to 1:01.

9. As a compositionof matter, a polymerization catalyst consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and an arsine having the structural formula (R) Ar wherein R is a hydrocarbon radical selected from the group consisting of alkyl radicals containing 1-12 carbon atoms and phenyl, the molar ratio of titanium tetrachloride to arsine being within the range of 1:1 to 1:01

10. As a composition of matter, a polymerization catalyst consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and triphenyl amine, the molar ratio of titanium tetrachloride to triphenyl amine being withinthe range of 1:1 to 1:0.1.

11. As a composition of matter, a polymerization catalyst consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and triphenyl stibine, the molar ratio of titanium tetrachloride to triphenyl stibine being within the range of 1:1 to 1:01.

12. As a composition of matter, a polymerization catalyst consisting essentially of a prereacted mixture of metallic aluminum and titanium tetrachloride and triphenyl arsine, the molar ratio of titanium tetrachloride to triphenyl arsine being with the range of 1:1 to 1:01.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE POLYMERIZATION OF PROPYLENE TO FORM SOLID CRYSTALLINE POLYMER, THE IMPROVEMENT WHICH COMPRISES EFFECTING THE POLYMERIZATION IN LIQUID DISPERSION IN AN INERT HYDROCARBON LIQUID AND IN THE PRESENCE OF A CATALYTIC MIXTURE CONSISTING ESSENTIALLY OF A PREREACTED MIXTURE OF METALLIC ALUMINUM AND TITANIUM TETRACHLORIDE AND AN AMINE HAVING THE STRUCTURAL FORMULA (R'')3N WHEREIN R'' IS A HYDROCARBON RADICAL SELECTED FROM THE GROUP CONSISTING OF ALKYL RADICALS CONTAINING 1-12 CARBON ATOMS AND PHENYL, THE MOLAR RATIO OF TITANIUM TETRACHLORIDE TO AMINE BEING WITHIN THE RANGE OF 1:1 TO 1:0.1. 